1. Field of the Invention
The present invention relates to a plasma processing apparatus employing a plasma to form a thin film on a surface of a sample, etching a surface of a sample, and the like.
2. Description of the Background Art
A conventional radio frequency (RF) plasma processing apparatus with parallel plates has been widely used as an apparatus using a plasma to process a sample, such as a substrate, a semiconductor wafer (simply referred to as a "wafer" hereinafter), in a processing chamber thereof. In this plasma processing apparatus, an RF power is applied to one or both of electrodes to generate a plasma between the electrodes and a self-bias voltage between the plasma and a sample allows ions to be introduced into a surface of the sample. This plasma processing apparatus is configured to form a thin film through plasma CVD, provide etching process, and the like.
For the above-mentioned parallel plate RF plasma processing apparatus, however, it is difficult to achieve required fine pattern formation and damage reduction associated with high integration and performance of semiconductor devices. In other words, in order to implement such processes, it is important to generate and control a low-pressure high-density plasma. Furthermore, the plasma should be uniform over a large area to process a wafer of a large diameter.
To satisfy such demands, various plasma sources have been proposed and applied to semiconductor processes. In particular, an inductively coupled plasma apparatus employing an RF antenna 7, as shown in FIG. 11, may be applied to semiconductor processes since the apparatus can relatively simply be constructed and is also capable of generating a low-pressure high-density plasma.
In the apparatus, as shown in FIG. 11, that side of a processing chamber which is opposite to a sample mounting stage 4 is constructed of a dielectric window 18 made, e.g., of quartz glass. Dielectric window 18 has an external surface having mounted thereto RF antenna 7 comprised of a planar, spiral coil. An RF electric field is radiated in processing chamber 2 through RF antenna 7. By allowing electrons present in the electromagnetic field to collide with neutral particles of processing gases, the processing gases disociate ions and neutrals, resulting generation of a plasma. Ions in the plasma are accelerated toward a sample by an RF bias voltage independently applied to sample mounting stage 4 and the ions are thus introduced into a sample to form a thin film, provide an etching process, and the like.
For the above-mentioned inductively coupled plasma processing apparatus used to form a thin film, provide etching process, and the like, dielectric window 18 of quartz glass or the like existing between RF antenna 7 and a generated plasma degrades the transmission efficiency of an RF power to the plasma. Accordingly, the power applied to RF antenna 7 should be increased to obtain a low-pressure high-density plasma.
Furthermore, the phenomenon that plasma density rapidly increases at more than an RF power (i.e., a mode jump phenomenon) is frequently observed and processing conditions can thus be disadvantageously limited.
Furthermore, the ionized species, reaction products and the like of the processing gases can be deposited on an internal surface of dielectric window 18 and ions can sputter dielectric window 18 and thus vary its thickness, so that L and C matching circuits formed via dielectric window 18 can change to disadvantageously vary a discharge condition. In particular, a conductive film deposited on dielectric window 18 can cause short-circuit of an RF electric field.
Furthermore, dust particles can be produced from a film deposited on dielectric window 18 by ion sputtering on, dielectric window 18, or the like.
Furthermore, if a grounded electrode (not shown) for an RF bias voltage applied to a sample is provided around mounting stage 4, the bias is not uniformly applied to the sample, often disadvantageously resulting in uneven processing rate. In particular, in the case that the grounded electrode is far from a sample, an arc discharge can be occurred between the stage and other grounded metallic parts of the apparatus.